Gastric adenocarcinoma is the second leading cause of cancer-related death in the world. Helicobacter pylori is the strongest identified risk factor fr this malignancy, yet only a fraction of colonized persons ever develop neoplasia. One H. pylori determinant associated with increased gastric cancer risk is the cag pathogenicity island, and several cag genes encode components of a type IV secretion system which exports bacterial proteins such as CagA into host epithelial cells. Our group has now demonstrated that H. pylori cag+ strains selectively activate -catenin, the EGF receptor (EGFR), and spermine oxidase (SMO), host effectors that influence carcinogenesis, in gastric epithelial cells. We have also demonstrated that environmental factors associated with gastric cancer, such as iron deficiency and salt, augment the ability of H. pylori cag+ strains to induce gastric cancer. Therefore, the overarching objective of this Application is delineation of the molecular signaling events initiate by H. pylori:epithelial cell contact that regulate phenotypes related to gastric carcinogenesis. This PPG will integrate studies of host-pathogen interactions initiated by biomedical researchers who have made a strong and clear commitment to research within the fields of gastroenterology, cancer biology, carcinogenesis, and microbiology, and will generate results that would not be attainable through independent investigation. The component Projects are driven by discrete hypotheses, yet are cohesive in that each focuses on H. pylori:epithelial interactions that induce cellular responses with carcinogenic potential. The individual projects include: Project 1. Role of iron and -catenin activation in gastric carcinogenesis (Pi-Richard Peek). Project 2. EGFR activation and polyamines in H. pylori-induced gastric cancer (Pi-Keith T. Wilson). Project 3. Regulation of H. pylori virulence by dietary factors that impact gastric cancer (Pi-Timothy Cover). The efforts of each Project will be further unified by dynamic interactions with Specific Core facilities, which include the Gastric Histopathology Core (Core A), the Proteomics Core (Core B), and an Administrative Core (Core C). By maintaining a grounded focus on fundamental interactions that occur at the H. pylori:epithelial interface, results from this proposal will not nly improve our understanding of gastric cancer, but will also identify potential therapeutic targets for prevention and more effective treatment of this disease.